The conventional exercise bicycle body (as shown in FIGS. 1 and 2) has a control for magnetic resistance constructed on the bicycle frame 11 which is fastened pivotally with the magnetic wheel 12. The magnetic wheel 12 is lined with a non-magnetic layer 13 on the rim. The arc-shaped seat for magnets 15 with magnetic pieces 14 is fixed at an interior edge of the bicycle frame 11 beneath the magnetic wheel 12. The arc-shaped seat 15 uses an adjustment device 16 to adjust the space between the magnetic pieces 14 and the magnetic wheel 12 for controlling and damping the force of turning the magnetic wheel (as shown in FIGS. 3 and 4).
However, such construction as described above is defective in design because the surface of the magnetic wheel 12 still needs to be lined with a non-magnetic layer 13. Therefore, if the lining of the non-magnetic layer 13 is not stable, then it will easily fall off; and furthermore, if the curvature of the lining of the non-magnetic layer 13 is different from the magnetic wheel 12, then it will affect the rotational inertia of the magnetic wheel 12, or even rub against the magnets of the arc-shaped seat 15.
In addition, because the magnetic wheel 12 and arc-shaped seat 15 are fastened on the bicycle frame 11, the positioning causes the magnetic wheel 12 to be able to be easily deviated from its pivoting place on the frame 11 after being used over a long period of time; and furthermore, it causes the free space between the magnetic wheel 12 and the arc-shaped seat 15 to change such that the adjustment device 16 is not able to accurately change and control the magnetic resistance of damping force.